Timing and sequencing circuit



Nov. 24, 1953 J- J. RILEY ET AL TIMING AND SEQUENCING CIRCUIT Filed Oct.19, 1951 INVENTORS JOSEPH J. RILEY RICHARD ALM ATTORNEY Patented Nov.24, 1953 TIMING AND SEQUENCING CIRCUIT Joseph J. Riley and Richard Aim,Warren, Ohio, assignors to The Taylor-Winfield Corporation, Warren,Ohio, a corporation of Ohio Application October 19, 1951, Serial No.252,148

11 Claims.

The present invention relates to electronic timing and control circuits,and more particularly to an improved and simplified electronic sequencecontrol timer for use in electric resistance welding machines and thelike.

An object of the present invention resides in the provision ofelectronic timing circuit for timing and controlling a plurality ofsequentially related operations or control phases, wherein certain novelcircuit arrangements are utilized to insure accurate and thoroughlydependable performance regardless of substantial variations in the linevoltage applied thereto. By the teachings of our invention this may beaccomplished without ancillary voltage control and regulation equipmentas will appear.

Another object of the present invention is the provision in a timingcircuit for timing a plurality of sequentially related control phases,of an arrangement whereby a particular phase of control is regulated insuch manner that deleterious results are avoided in the event ofuntimely breakdown of certain of the circuit components.

More specifically the present invention seeks to provide a controlcircuit utilizing a plurality of electronic discharge devices arrangedfor sequentially related timed periods of conduction, wherein afterinitiation of conduction in certain of the discharge devices, thetermination of conduction therein after a predetermined time interval iswholly independent of subsequent initiation of conduction in certainother of said sequentially related discharge devices. Thus, for example,in using our timer for controlling electric resistance weldingapparatus, the weld time period may be initiated and terminated by thesame means, whereby should the said means fail to function the weld timeperiod will not be initiated, or if initiated, will terminate.

Another object of the present invention is the provision in anelectronic timing circuit, particularly for use in controllingsequential operations of electric resistance welders, of an improvedmeans, operative upon termination of the weld time" period, to preventuntimely reinitiation of said period during subsequent sequentialoperations of the same cycle.

Yet another object of the present invention is the provision of a novelelectronic control circuit for controlling a plurality of sequentiallyrelated operations wherein a minimum number of electric dischargedevices is required to control a given number of sequential operations.

Ancillary objects of the invention include the provision of anelectronic control circuit having the above enumerated characteristicswhich is inexpensive to produce, does not require a direct current powersource, and in which each of the electric discharge devices used may beof the same style and size to facilitate maintenance and repair.

Other objects and advantages of the invention will become apparent uponfull consideration of the following detailed specification andaccompanying drawing wherein is illustrated a certain preferredembodiment of our invention.

The sole figure of the drawing is a schematic representation of acontrol circuit constructed according to the teachings of our inventionand associated with conventional electric resistance welding equipment.

In the drawing, the reference numeral l0 designates a commercialalternating current power source, to which is connected the primarywinding of a transformer H. The secondary of the transformer II isprovided with terminals I 2 and i3, and center tap I 4', connectingrespectively conductors l2, l3 and I4. Connected between conductors l2and I are, in series relation, a gaseous discharge device I5, relay I5and a starting switch H, the latter preferably being of the type whichis controllable by the foot of the machine operator. As will beobserved, closing of switch I! will energize discharge device 15 andthus cause relay l6 to close. Contacts lia of relay It, in cooperationwith conductors l8 and I9, form a holding circuit in parallel with theswitch I! whereby the latter may be but momentarily closed to initiate acycle of operations. Contacts Hic of relay [6 connect conductors 20 and2| leading to a mechanical control panel 22, and in the illustratedapplication of the control circuit it is contemplated that the closingof contacts lic will cause movement of welding electrodes 23 toward andinto contact with workpieces 24. In accordance with usual practicecapacitor 34 and resistor 35 are provided in shunt relation to relay l5whereby energy may be stored during the conducting half-cycle ofdischarge device l5 and discharged through the relay during alternatenon-conducting half-cycle whereby the relay will be maintained in anenergized condition.

Closing of contacts 16b connects conductor I! to conductor 25 andaccordingly applies anodecathode voltage to another gaseous dischargedevice 26 which will then flre upon proper conditioning of its controland screen grids as will be apparent. In the resistance welding art itis desirable to provide a certain time interval or squeeze time betweenthe moving of electrodes 23 into contact with the workpieces 24 and thesubsequent application of welding energy thereto. Accordingly it ispreferable to condition the con trol grid of discharge device 26 with anormally negative hold-off signal whereby the same will be maintained ina non-conductive state for a predetermined time interval after theclosing of relay l6. This may be accomplished by providing a timeconstant network, comprising capacitor 21, resistor 28 and potentiometer23, in the grid circuit of discharge device 26, which circuit isconnected to conductor I2. To charge the capacitor 21 we have providedconductor 30 and resistors 3i and 32 which are connected betweenconductors l4 and 25; the arrangement being such that the cathode ofdischarge device 26 is in communication with conductor I4 throughresistors 3i and 32 whereby before contacts l6b are closed capacitor 21becomes charged through grid rectification of discharge device 26. Thecharge assumed by capacitor 21 provides a highly negative grid signalfor discharge device 26 upon closing of contacts I61), and the latterwill accordingly remain non-conductive until the charge has beensufiiciently dissipated through resistor 26 and potentiometer 23.

For additional control of discharge device 26 we have connected thescreen grid thereof to conductor 36 at a point between resistors 31 and32. A positive and iii-phase bias signal is thus provided which issuflicient to fire the discharge device 26 as it approaches a conductivestate through dissipation of its negative control grid bias. Thisfeature insures that firing will take place at the proper point in theapplied anodecathode voltage cycle, but does not otherwise efiect thetiming.

Connected in series with the anode of discharge device 26 is a relay 33,normally open contacts 33a of which are connected in series with thecathode of another discharge device 36. Relay 33 is energized uponinitiation of conduction in discharge device 26, and according to theprinciples of our invention the resulting closing of contacts 33aapplies anode-cathode potential to discharge device 36 to immediatelyinitiate conduction therein. A relay 3'! which is connected in serieswith the anode of discharge device 36 thus becomes energized andnormally open contacts 33a thereof close to connect conductors 36 and 39leading to a conventional weld current contactor 46; it beingcontemplated that the connecting of the last mentioned conductors 36 and39 will energize the contactor 46 to permit welding energy to pass tothe electrodes 23 to perform a weld.

Since the flow of weld current is thus directly dependent uponconduction in discharge device 36, weld time" may be controlled bytiming the duration of conduction of the said device 36. For thispurpose we have provided a control grid circuit comprising resistor 41,potentiometer 42, capacitor 43 and normally open contacts 33?). Thiscircuit is referenced to the cathode of discharge device 36 throughresistor 44 and conductor 45, as shown. A highly positive initial signalis desired so that the device 36 will fire immediately upon energizationof relay 33 and closing of contacts 33a and for this purpose we haveconnected capacitor 43, through normally closed contacts 33c and 33d. toa. fullwave direct current charging circuit comprising conductors 46 and41, rectox units 43 and 46, and capacitor 64.

[iii

As will be observed the arrangement is such that with relay 33 in adeenergized condition, capacitor 43 is disconnected from the controlgrid circuit for discharge device 36 and is connected to the terminalsof the above described direct current charging circuit. Upon relay 33being energized by firing of discharge device 26 contacts 330 and 33dopen and, contacts 33b close, simultaneously disconnecting capacitor 43from its charging circuit and connecting it into the control gridcircuit for discharge device 36. It will he noted that the chargeexisting in capacitor 43 impresses a highly positive grid signal on thedischarge device 36, and the latter, having anodecathode potentialapplied thereto by the closing of contacts 33a, begins to conductimmediately. The charge of capacitor 43 dissipates according to the R-Ctime constant factor of the network 4!, 42 and 43 so that after apredetermined period the discharge device 36 will have substantially nopositive signal from capacitor 43. To insure that the discharge device36 ceases to conduct after such predetermined period we have impressed asecond signal upon its control grid which has the effect of referencingthe positive signal of capacitor 43 to a potential below that of thecathode of discharge device 36. Thus as the charge on capacitor 43dissipates to a low value the control grid of discharge device 36 willbecome negative with respect to its cathode and will accordingly preventfurther conduction. The last mentioned signal is provided by means of apotentiometer 5| which is connected at one side to the cathode ofdischarge device 36 and at the other side to the anode of dischargedevice 26; the arrangement being such that a voltage drop appears acrossthe terminals of potentiometer 5i when discharge device 26 isconducting. It will be noted that the potential of the anode ofdischarge device 26, when the latter is conducting, will be negativewith respect to the cathode of discharge device 36, and thus, bysuitably adjusting the sliding tap of potentiometer 5| and connectingthe same in the control grid circuit for discharge device 36 we providea negative reference bias therefor. As is indicated by the drawing it ispreferable to connect a capacitor 62 in parallel with potentiometer 5|to partially filter the periodical voltage impulses appearingthereacross, and to include a rectox unit 63 between last mentionedcapacitor 52 and the anode of discharge device 26 to undesirablefeedback of the charge upon capacitor 62.

Since accurate and dependable control of the weld time is an importantconsideration we have provided a third control signal for dischargedevice 36, which is applied to the screen grid thereof and is operativeto effect a "cut-off" control to assist in terminating conduction indischarge device 36 and to prevent subsequent untimely refiring thereofafter the "weld time period. In the illustrated embodiment of the rinvention we have connected a capacitor 54 and resistor 55 across theterminals I2 and I3 of power transformer ll. Connected between the saidcapacitor 54 and resistor 55 is a conductor 56 which is associated withthe screen grid of discharge device 36 by means of conductor 51. Thecomparative values of capacitor 54 and resistor 55 are such that analternating potential appears across conductors 56 and M which issubstantially reversed in polarity with respect to that appearing acrossconductors I2 and I4, but is lagging in phase relationship byapproximately twenty electrical degrees. Thus, assuming discharge device36 to be conducting and its positive control grid bias from capacitor 43to have been substantially dissipated whereby termina- 'tion ofconduction is impending, there is an interval of about one-fifteenth toone-twentieth of a full electrical cycle after the beginning of apositive half-cycle of anode-cathode potential wherein discharge device36 must fire. At the end of this interval the screen grid signal becomesnegative with respect to the cathode to prevent sponsive control overthe discharge device, easily overcomes the effect of the screen signal.

The cut-off and lock-out" screen grid control as above set forth formsan important part of this invention since it prevents accidentaltriggering of discharge device 36 after the "weld time period, andperhaps more important, insures that the discharge device, if itconducts at all, will conduct over substantially the entire half cycle.Being thus able to positively predict the performance of dischargedevice 36, it is possible to effectively prevent the occurrence of highcurrent transients in the welding apparatus as will be understood.

After completion of a weld it is customary to hold the electrodes 23 inpressure contact with the work 24 for a certain period (hold time)wherein the workpieces become properly fused together. Thus in thesequencing timer herein illustrated we have provided means which areoperative to cause retraction of the electrodes 23 a predetermined timeafter the termination of the weld time period. The means referred toincludes a discharge device 58, the anode of which connects conductor l4through potentiometer 55 and resistor 68, and the cathode of which isconnected to contacts lGa or relay l8 through a switch 6|. A conductor63 connects the anode of discharge device 58 with the control grid ofdischarge device l whereby a ighly negative signal is impressed upondischarge device I5 when discharge device 58 is conducting. A capacitor62 is connected in parallel with resistor 68 and potentiometer 59whereby the pulsating energy passed by discharge device 58 may be storedso that the control grid signal impressed upon discharge device i5 is ofa relatively non-pulsating nature.

With the arrangement thus described it will be understood that bycausing discharge device 58 to become conductive, discharge device l5will be rendered non-conductive, deenergizing relay IE to causeretraction of the electrodes 23 and to end a welding cycle. To firedischarge device 58 at the proper time we provide another dischargedevice 64, the cathode of which is connected to conductor i4, and theanode of which is con nected to conductor 12 through a time constantnetwork comprising resistors 65 and 66, potentiometer 61 and capacitor68. Discharge device 64, being in direct communication with the powertransformer H begins to conduct immediately upon power being appliedthereto from the source and accordingly maintains a full charge oncapacitor 68. Thus, by connecting the control grid of discharge device58 to the anode of discharge device 64, we provide that discharge device58 will be maintained in a non-conductive state at 6 all times whendischarge device 64 is conducting, and that upon the last mentioneddischarge device being rendered non-conductive, discharge device 58 willbe fired after a predetermined delay period wherein the charge uponcapacitor 68 is dissipated.

Preferably discharge device 64 is rendered non-conductive at the end ofthe weld time period and in the illustrated embodiment of our inventionwe effect this by connecting the screen grid of discharge device 64,through conductors 69 and 18, to the negative terminal of capacitor 52,whereby when discharge device 26 is conduct ing a highly negative screengrid signal will be impressed upon discharge device 64. An impulsetransformer H, the secondary of which is connected in series withconductor 69 and the primary of which is connected in parallel withrelay 31, impresses a positive signal upon the screen grid of dischargedevice 64 while discharge device 36 is conducting, and it will beunderstood that when discharge device 36 stops conducting. ending theweld time period, discharge device 64 will be immediately extinguishedby the negative screen grid signal from capacitor 52. Hold time is thenprovided by charged capacitor 88 which must be discharged through thenetwork associated therewith before discharge device 58 begins toconduct.

In the illustration, switch BI is set for nonrecycling operation. Bythis arrangement the cathode of discharge device 58 may be connected tothe power conductor [2 through contacts l6a of relay l3 and through footswitch I'I. Thus assuming foot switch I! to be open, discharge device 58will conduct but momentarily to extinguish discharge device I5 anddeenergize relay I5. When relay [6 is deenergized, anode-cathodepotential is removed from all discharge devices with the exception ofdischarge device 64 which again begins to conduct to charge capacitor68. To initiate a new cycle the machine operator must close foot switchI! whereby the sequence of operations takes place in the usual manner.

In the event that the operator inadvertently holds the foot switch I]closed too long, anodecathode potential will be applied to dischargedevice 58 even though relay I6 is deenergized. Thus a hold-oil bias ismaintained on discharge device I5 and the latter cannot fire to initiatea new cycle. Discharge device 64 must also be maintained non-conductiveduring this time and to accomplish this we have connected its controlgrid, through switch BI, to the anode of discharge device 58. Thenegative signal provided thereby takes the place of the negative screensignal which is removed when relay IB is deenergized to extinguishdischarge device 26. It will thus be apparent that even though switch (Iis held closed, a new cycle of operations cannot be initiated until theswitch H is opened to extinguish discharge device 58 and then reclosedto fire discharge device l5.

For automatic recycling operation switch BI is moved to the other of itsindicated operative positions whereby the cathode of discharge device 58is connected to contacts IBb of relay l6 and the control grid ofdischarge device 64 is connected to the anode of discharge device l5.Switch i1 is held closed by the operator or if desired by other suitablemeans, not shown. Thus, when discharge device 58 fires to renderdischarge device [5 non-conducting a highly positive signal is placed onthe control grid of genes discharge device 64 from the anode ofdischarge device It. Discharge device 64 accordingly fires immediatelyto charge capacitor 68. Discharge device 58 fires but momentarily sinceits anodecathode potential is removed when relay I6 is deenergized, andthus discharge device l will refire to initiate a new cycle after apredetermined ofi' time period wherein the charge on capacitor 82 isdissipated to remove the control grid hold-ofi bias therefrom. Recyclingmay, oi course, be discontinued at any time by merely opening switch ll.

As will be understood, in non-recycling operation oil-time is notincluded as one of the sequentially related control periods since insome instances it is desirable to initiate a new cycle of operationssubstantially instantaneously upon the termination of a preceding cycle.To efiect such instantaneous reinitiation of cycles the charge oncapacitor 62, which provides a negative bias for extinguishing dischargedevice l5, must be rapidly dissipated to remove such negative bias andpermit discharge device ii to reflre as soon as possible. For thispurpose we have provided. in parallel with capacitor 62, a lowresistance discharge path including switch 61 and resistors l4 and 15.The arrangement is such that when switch 6| is set for non-recyclingoperation low value resistances l4 and 15 are in parallel with capacitor62 and the charge thereon may thus be quickly dissipated through thesaid resistances I4 and 15 as well as through resistances 59 and 66.When switch 6| is set for au tomatic recycling operation the lowresistance path is interrupted whereby capacitor 62 discharges throughresistors 59 and Eli in the usual manner to provide the desiredpredetermined "of! time" period.

For set-up work and test operations wherein it is not desirable toenergize the weld contactor 40, switch 12 may be moved to disconnectrelay 31 and substitute in its place a resistance 13 of equivalent loadvalue. The overall operation of the control circuit is not affected.

It should now be apparent that we have accomplished the objectsinitially set forth. The novel control circuit herein described in itspreferred form, utilizes but five electronic discharge devices to obtainaccurate and dependable control of four sequentially related periods oitimed duration; i. e., "squeeze time, "weld time, hold time" and offtime. The timing accuracy of our control is subject to negligiblevariation regardless oi relatively wide variations in the potentialsupplied by the source In. This we have accomplished by providingcapacitor-potentiometer time constant networks to control each oi thetime periods, each of which networks operates on a discharging R-C timecurve. This arrangement is inherently accurate as will be understoodsince the discharge time remains substantially constant over wide rangesof capacitor charge.

For controlling the critical weld time period we have provided meanswhich operate independently of any of the discharge devices to time outand extinguish discharge device 36. In this respect it will beparticularly noted that charged capacitor 43 renders discharge device 36conductive by placing a highly positive control grid signal thereon, andthen renders it again non-conductive as the charge is dissipated. Thismethod of operation is for all practical purposes tool-proof in thatcapacitor 43 must be connected into the control grid circuit to firedischarge device 38 and thus necessarily assures that the latter will berendered non-conductive at the proper time. Should relay 3! for anyreason hecome deenergized whereby capacitor 43 would be disconnectedfrom the grid circuit 0! discharge device 36, the anode-cathodepotential is also removed to prevent further conduction. Thus anyuntimely breakdown of the circuit components, ii such is to affect theweld time" period at all, will cause it to end prematurely, and will inno instance cause overtiming oi the period whereby the work and/ormachine might be severely damaged.

In addition to the novel time control arrangement described above wehave further provided a synchronized cut-ofi control which insures thatdischarge device 36 will conduct over substantially the entire halfcycle, or not at all. This control is effected by providing aphase-shiited screen grid signal which is generally opposite in polarityto the anode potential of discharge device 36, but which is lagging inphase relation by approximately twenty electrical degrees. Thus, if thecontrol grid signal is not sufiiciently strong to trigger the dischargedevice in the first portion of the anode potential cycle it cannotthereafter cause conduction due to the opposing negative signal appliedon the screen grid. With this arrangement we assure conduction over afull halt cycle whereby undesirable transient currents in the weldingapparatus may be minimized. It will also be noted that the cut-offcontrol provided by our circuit will have no effect on the operation ofdischarge device 36 until the "weld time" has been substantially timedout by discharge of capacitor 43. The cut-oil signal may thus be appliedcontinuously to discharge device 36 as in the illustrated circuit.

Our timer finds inherent advantages in the use of alternating current inthat relays i6, 33 and 31 are each operated by half-wave rectifyingdischarge devices and it is thus assured that the said relays will beenergized on a cycle of one polarity only. Design considerations of thecircuit are thereby minimized since transient currents are more easilyavoided. The use of alternating current is further avantageous in thatit is readily available from commercial sources whereas direct currentpower must ordinarily be supplied by providing additional rectifying andregulating components in the control circuit. Initial investment andmaintenance expense are accordingly higher in the latter case.

The above specifically described embodiment should be considered asillustrative only, and reference should be had to the appended claims indetermining the true scope of our invention.

We claim 1. In a control circuit for controlling a plurality ofsequentially related operations of a welding machine of the type havingelectrodes, means to move said electrodes, and a contactor forcontrolling the flow of weld current to said electrodes; the combinationof an alternating current power source, a first grid-controlled gaseousdischarge device connected to said power source, a switch for energizingsaid first discharge device, a first switchin relay adapted to beenergized in response to conduction in said first discharge device, saidmeans to move being operative upon energization of said relay to movesaid electrodes into contact with workpieces to be welded, a secondgaseous discharge device connected to said power source through normallyopen contacts of said first relay, said second discharge device beingconnected in anti-parallel relation to said first discharge device, acontrol grid circuit for said second discharge device including acapacitor-potentiometer time constant network, means operative prior toenergization of said first relay to charge said capacitor whereby anegative grid signal is placed on said second discharge device tomaintain the same non-conductive, the arrangement being such that saidcapacitor will begin to discharge upon energizetion of said first relayto render said second i discharge device conductive a predetermined timethereafter, a second relay adapted to be energized in response toconduction in said second discharge device, a third gaseous dischargedevice connected to said source through normally open contacts of saidfirst and second relays, a control grid circuit for said third dischargedevice including a capacitor-potentiometer time constant network, saidlast mentioned network including normally open contacts of said secondrelay, means for charging said capacitor whereby when said lastmentioned normally open contacts are closed a positive grid signal isplaced on said third discharge device to render the same conductive,said charging means including normally closed contacts of said secondrelay, a third switching relay adapted to be energized in response toconduction in said third discharge device, means responsive to theenergization of said last mentioned relay to energize said contactor, I;

a fourth gaseous discharge device connected to said power source inparallel relation to said third discharge device, a screen grid circuitfor said last mentioned discharge device including impulse translatingmeans operative in response to conduction in said third discharge deviceto place a positive screen grid signal on said fourth discharge deviceand means operative in response to conduction in said second dischargedevice to place an opposing negative signal on said fourth dischargedevice, said last mentioned positive signal being of greater magnitudethan said opposing negative signal, a capacitor-potentiometer timeconstant network connected in series with the anode-cathode circuit ofsaid fourth discharge device, a fifth gaseous discharge device connectedto said source through normally open contacts of said first relay, saidfifth discharge device being connected in anti-parallel relation to saidfourth discharge device, a control grid circuit for said fifth dischargedevice including conductor means connected to said last mentioned timeconstant network, the arrangement being such that when said fourthdischarge device is conducting and for a predetermined time thereafter anegative grid signal is placed on said fifth discharge device to renderthe same nonconductive, and a control grid circuit for said firstdischarge device including conductor means connected to the anode ofsaid fifth discharge device whereby a negative grid signal is placed onsaid first discharge device when said fifth discharge device isconducting.

2. In a control circuit for timing a plurality of sequentially relatedoperations the combination of a power source, a first gaseous dischargedevice connected to said source, a switch for energizing said firstdischarge device, a switching relay adapted to be energized in responseto conduction in said first discharge device, a second gaseous dischargedevice connected to said source through normally open contacts of saidfirst relay, said second discharge device being connected inanti-parallel with said first discharge device, a control grid circuitfor said second disi0 charge device including a capacitor-potentiometertime constant network, means for chargin said capacitor while said firstrelay is deenergized whereby a negative grid signal is placed on saidsecond discharge device, a second switching relay adapted to beenergized in response to conduction in said second discharge device, athird gaseous discharge device connected to said source through normallyopen contacts of one of said relays, a grid circuit for said seconddischarge device including a capacitor-potentiometer time constantnetwork and normally open contacts of said second relay, means to chargesaid last mentioned capacitor including normally closed contacts of saidsecond relay, the arrangement being such that when said last mentionednormally open contacts are closed a positive control grid signal isplaced on said third discharge device, means cssociated with said lastmentioned grid circuit and said second discharge device operative whensaid second discharge device is conducting to place a negative controlgrid bias on said third discharge device, said positive signal beinginitially of greater magnitude than said negative bias, and meanresponsive to the cessation of conduction in said third discharge deviceand operative a predetermined time thereafter to terminate conduction insaid first discharge device.

3. Apparatus according to Claim 2 further characterized by said thirddischarge device having a screen grid and control circuit therefor, saidcontrol circuit including phase shifting means associated with saidsource adapted to place a screen grid signal on said third dischargedevice which is generally reversed in polarity to the anode-cathodepotential of said third discharge device and is lagging in phaserelationship by an angle in the order of twenty electrical degrees, thearrangement being such that if said third discharge device is notrendered conductive by said control grid signals in the first portion ofthe anode-cathode potential cycle said screen grid signal willthereafter prevent conduction therein for the remaining portion of thecycle.

4. In a control circuit for welding apparatus of the type havingelectrodes movable toward and away from work pieces and a weld contactorfor controlling the flow of weld current, the combination of a powersource, a switching relay, means for energizing said relay, a firstgaseous discharge device connected to said source through normally opencontacts of said relay, means associated with said relay operative uponenergization thereof to cause said electrodes to move into contact withsaid workpieces, a grid control circuit for said first discharge deviceincluding a capacitor-potentiometer time constant network, meansassociated with said sourc and said time constant network adapted tocharge said capacitor when said relay is deenergized whereby a negativegrid signal is placed on said first discharge device, the arrangementbeing such that said charging means are rendered ineffective uponenergization of said relay whereby said capacitor is discharged torender said first discharge device conductive a predetermined timesubsequent to energization of said relay, a second switching relayadapted to be energized in response to conduction in said firstdischarge device, a second gaseous discharge device connected to saidsource through normally open contacts of one of said relays, switchingmeans operative in response to conduction in said second dischargedevice to energize said weld contactor, a control grid circuit for saidsecond discharge device including a capacitor-potentiometer timeconstant circuit and normally open contacts of said second relay,charging means for said last mentioned capacitor including normallyclosed contacts of said second relay, the arrangement being such thatwhen said second relay is energized a positive control grid signal isplaced on said second discharge device, means associated with said lastmentioned control grid circuit and said first discharg device operativein response to conduction in said first discharge device to place anegative control grid bias on said second discharge device, saidpositive signal being initially of greater magnitude than said negativebias, and means responsive to the termination of conduction in saidsecond discharge device and operative a predetermined time thereafter todeenergize said first re- Apparatus according to claim 4 furthercharacterized by said means responsive to the termination of conductionin said second discharge device comprising a third gaseous dischargedevice connected to said source, means associated with said first andthird discharge devices operative in response to conduction in saidfirst discharg device to place a negative grid bias on said thirddischarge device, means associated with said second and third dischargedevices operative in response to conduction in said second dischargedevice to place a positive grid signal on said third discharge device,said positive grid signal being of greater magnitude than said negativegrid bias, and means associated with said third discharge devic and saidfirst relay operative in response to termination of conduction in saidthird discharge device to deenergize said first relay a predeterminedtime thereafter.

6. In a control circuit for electric resistance welding apparatus of thetype having a weld contactor adapted to control the flow of weld currentthe combination of a source of pulsating power, a gaseous dischargedevice having an anode, cathode and control grid, said anode and cathodebeing connected to said power source, switching means for controllingthe application of anode-cathode potential to said discharge device, acontrol grid circuit for said discharge device including acapacitor-potentiometer time constant network, means to charge saidcapacitor, switching means for said control grid circuit having normallyclosed contacts connecting said capacitor withsaid charging means, andnormal- 1y open contacts connecting said capacitor with said grid, thearrangement being such that when said normally open contacts are closeda positive control grid signal is placed on said discharge device tocause conduction therein, means associated with said grid circuitoperative when said switching means is energized to place a negativegrid bias on said discharge device, said positive signal being initiallyof greater magnitude than said negative bias, switching means associatedwith said discharge device operative in response to conduction thereinto energize said weld contactor.

'1. Apparatus according to claim 6 further characterized by saiddischarge device having a screen grid, means associated with said screengrid and said source of power adapted to place a control signal on saidscreen grid, said control signal being generally opposltein polarity tosaid anode-cathode potential and lagging in phase relationship by anangle in the order of twenty electrical degrees, the arrangement beingsuch 12 that if said positive signal does not cause can duction in saiddischarge device within the initial portion of the anode-cathodepotential wave said screen signal will prevent conduction during theremaining portion of the wave.

8. Apparatus according to claim 6 further in cluding a second dischargedevice connected to said source, means to energize said second dischargedevice and said switching means for con-- trolling the application ofanode-cathode potential to said first mentioned discharge device andsaid means to place a negative grid bias upon said first mentioneddischarge device being operative in response to conduction in saidsecond discharge device.

9. In a control circuit for electric resistance welding apparatus of thetype having electrodes movable toward and away from workpieces and aweld contactor for controlling the flow of weld current, the combinationof a source of power, means to cause said electrodes to move into con--tact with said workpieces, said means including a first gaseousdischarge device, a second gaseous discharge device connected to saidpower source and adapted to be energized a predetermined time aftermovement of said electrodes into contact with said workpieces, a thirdgaseous discharge device having an anode, cathode and grid, said anodeand cathode being connected to said source, a grid circuit for saidthird discharge de vice having a resistance member therein and acapacitor connectable into and out of said circuit in parallel with saidresistance member, switching means operative in response to conductionin said second discharge device to connect said capacitor into said gridcircuit, charging means for said capacitor, switching means normallyconnecting said capacitor to said charging means operative in responseto conduction in said secand discharge device to disconnect saidcharsing means, the arrangement being such that said capacitor whencharged and connected in said rid circuit will render said thirddischarge device conductive for a predetermined time interval whereinsaid capacitor discharges through said resistance member, and meansresponsive to conduction in said second discharge device dor applyinga'blocking control bias to said third discharge device, said blockingbias being operative to extinguish said third discharge device aftersaid predetermined time interval.

10. In a timing circuit for electric resistance welding apparatus of thetype having a weld contactor or controlling the flow of welding energythe combination of a gaseous discharge device or! the type having ananode, cathode and control grid, 9. source of alternating current powerconnecting said anode and cathode, a grid circuit for applying a controlsignal on said discharge device including a resistance member and acapacitor associated in parallel with said resist ance member, chargingmeans for said capacitor, switching means in said grid circuit havingnormally open and normally closed contacts, said charging means beingconnected to said capacttor through said normally closed contacts saidcapacitor being connected to said resistance member through saidnormallyopencontactsthe arrangement being such that said capacitor when chargedand connected to said resistance member will render said dischargedevice conductive for a predetermined time wherein said capacitordischarges through said resistance member, and means operativeresponsive to energization of said switching means to apply a 13blocking control bias to said discharge device, said blocking bias beingoperative to extinguish said discharge device after said predeterminedtime interval.

11. Apparatus according to claim 10 further including means to impress asecond control signal on said discharge device, said second controlsignal being generally reversed in polarity to said anode-cathodepotential and lagging in phase relationship by an angle in the order oftwenty electrical degrees, the arrangement being such that if said firstsignal does not render said discharge device conductive in the initialportion of the anode-cathode potential wave said second signal willprevent conduction during the remaining portion of said wave.

JOSEPH J. RILEY. RICHARD ALM.

References Cited in the file of this patent UNITED STATES PATENTS StadumMar. 25, 1952

